Mount Whitney, the tallest peak in the continental US at 14,494 feet, stands in the Sierra Nevada Mountains, which carry less snow than normal in 2008. The Sierra snowpack is vital to California water supplies.

Photo: David McNew, Getty Images

Mount Whitney, the tallest peak in the continental US at 14,494...

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Frank Gehrke, chief of snow surveys for the Department of Water Resources, stands in snow free meadow as he talks to reporters during the snow survey at Echo Summit Calif., Tuesday, May 1, 2012. Saying it's "not a surprise, especially considering the type of year we've had this year," Gehrke found no snow at the Echo Summit survey site. Warm spring weather combined with lower then normal precipitation, caused the statewide snowpack water content to be only 40 percent of normal for this time of year.

Photo: Rich Pedroncelli, Associated Press

Frank Gehrke, chief of snow surveys for the Department of Water...

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Frank Gehrke, chief of snow surveys for the Department of Water Resources, plunges the survey pole into the snowpack during the snow survey near Echo Summit Calif., Tuesday, Feb. 28, 2012. Despite recent storms the survey showed the snow pack to be only 17.7 inches deep, with a water content of only 3.9 inches_ which is only 16 percent of normal for this location at this time of the year.

Photo: Rich Pedroncelli, Associated Press

Frank Gehrke, chief of snow surveys for the Department of Water...

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Chief of the California Cooperative Snow Survey Frank Gehrke measuring 400 feet from the marker pole to do a manual survey off Highway 50 at Philllips Station near Echo Summit, Calif., on Tuesday, January 3, 2012. This and other manual and electronic surveys up and down the state will determine the amount of water in the early winter snowpack.

Photo: Liz Hafalia, The Chronicle

Chief of the California Cooperative Snow Survey Frank Gehrke...

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Frank Gehrke, chief of snow surveys for the California Department of Water Resources, removes the survey tube from the snowpack as DWR's David Todd, rear, looks on during the snow survey at Echo Summit, Calif., Wednesday, March 30, 2011. The survey showed the snow pack to be about 154 percent of normal for this time of the year.

The future of water for drinking and irrigation looks increasingly bleak throughout California and the world's northern regions as the changing global climate shrinks mountain snowpacks and speeds early runoffs, Stanford researchers forecast.

Decreases in winter snowpacks are likely to be most noticeable during the next 30 years and will continue to shrink through the century, according to an analysis of future climate trends by a team of specialists led by Noah Diffenbaugh at Stanford's Department of Environmental Earth System Science.

"One clear result is that western North America shows the most rapid and largest response to the continued emissions of greenhouse gases when it comes to early snowmelt and spring runoff," Diffenbaugh said.

The result, he and his colleagues say, will be less runoff water for irrigation during the season when California's high-value crops need it most for growing, and also more early springtime flooding that can strain dams and reservoirs before the water reaches lowland cities.

The researchers also found little cause for optimism from a survey of global warming's impact on the rest of the Northern Hemisphere, where literally billions of people depend on mountain snowpacks for drinking water and irrigation.

"Our results suggest that global warming will put increasing pressure on both flood control in the cold season and water availability in the dry season, and that these changes are likely to occur in some of the most densely populated and water-stressed areas of the planet," Diffenbaugh said.

Middle East impact

That vast region includes much of the northern Middle East and the mountains and deserts of Iraq, Iran and Afghanistan, where analysts have warned that population growth, coupled with the effects of global warming, pose fresh dangers of armed conflict and terrorism.

Northern Europe, India, Pakistan and China are also heavily dependent on winter snowfalls, and they will all see more and more years when the snowpack on the ground is lower than normal at the end of winter. The climate researchers calculated that by 2070 low-snow years will be the norm more than 80 percent of the time.

In their analysis the researchers noted that throughout the American West more years of "extremely low" winter snows and "extremely high" winter runoffs will mean "extremely low" runoff during each spring.

The result: a greater need for better flood control and reservoir capacity and an increased need for irrigation water at the very season when water supply is lowest for most "high-value" crops, they said.

Long process

But implementing the plans by changing rules for seasonal water releases from dams into reservoirs will require environmental impact approval studies and even congressional authorization, Jones said.

California is one of only nine states so far to develop comprehensive strategies and implement policies to deal with expected water shortages, droughts, shrinking snowpacks and other water-related problems if global temperatures increase this century as predicted by scientists, the Natural Resources Defense Council has reported.

Diffenbaugh's colleagues in the study include Stanford research assistant Martin Scherer and Moetasim Ashfaq, an atmospheric physicist at the Oak Ridge National Laboratory in Oak Ridge, Tenn. Their analysis is published in the current issue of the journal Nature Climate Change.